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* [Bug tree-optimization/68083] New: wrong code at -O3 on x86_64-linux-gnu
@ 2015-10-24 22:58 su at cs dot ucdavis.edu
2015-10-26 11:42 ` [Bug tree-optimization/68083] [6 Regression] " rguenth at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: su at cs dot ucdavis.edu @ 2015-10-24 22:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68083
Bug ID: 68083
Summary: wrong code at -O3 on x86_64-linux-gnu
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: su at cs dot ucdavis.edu
Target Milestone: ---
The current gcc trunk miscompiles the following code on x86_64-linux-gnu at -O3
in both 32-bit and 64-bit modes.
This is a regression from 5.2.x.
$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 6.0.0 20151023 (experimental) [trunk revision 229251] (GCC)
$
$ gcc-trunk -O2 small.c; ./a.out
$ gcc-5.2 -O3 small.c; ./a.out
$
$ gcc-trunk -O3 small.c
$ ./a.out
Aborted (core dumped)
$
------------------------------------
int a = 2, b = 1, c = 1;
int
fn1 ()
{
int d;
for (; a; a--)
{
for (d = 0; d < 4; d++)
{
int k;
if (c < 1)
if (k)
c = 0;
if (b)
continue;
return 0;
}
b = !1;
}
return 0;
}
int
main ()
{
fn1 ();
if (a != 1)
__builtin_abort ();
return 0;
}
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/68083] [6 Regression] wrong code at -O3 on x86_64-linux-gnu
2015-10-24 22:58 [Bug tree-optimization/68083] New: wrong code at -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu
@ 2015-10-26 11:42 ` rguenth at gcc dot gnu.org
2015-10-26 11:56 ` mpolacek at gcc dot gnu.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu.org @ 2015-10-26 11:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68083
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
Status|UNCONFIRMED |NEW
Last reconfirmed| |2015-10-26
Known to work| |5.2.0
Target Milestone|--- |6.0
Summary|wrong code at -O3 on |[6 Regression] wrong code
|x86_64-linux-gnu |at -O3 on x86_64-linux-gnu
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/68083] [6 Regression] wrong code at -O3 on x86_64-linux-gnu
2015-10-24 22:58 [Bug tree-optimization/68083] New: wrong code at -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu
2015-10-26 11:42 ` [Bug tree-optimization/68083] [6 Regression] " rguenth at gcc dot gnu.org
@ 2015-10-26 11:56 ` mpolacek at gcc dot gnu.org
2015-10-30 11:03 ` aoliva at gcc dot gnu.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2015-10-26 11:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68083
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |mpolacek at gcc dot gnu.org
--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Started with r226901.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/68083] [6 Regression] wrong code at -O3 on x86_64-linux-gnu
2015-10-24 22:58 [Bug tree-optimization/68083] New: wrong code at -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu
2015-10-26 11:42 ` [Bug tree-optimization/68083] [6 Regression] " rguenth at gcc dot gnu.org
2015-10-26 11:56 ` mpolacek at gcc dot gnu.org
@ 2015-10-30 11:03 ` aoliva at gcc dot gnu.org
2015-10-30 11:18 ` aoliva at gcc dot gnu.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: aoliva at gcc dot gnu.org @ 2015-10-30 11:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68083
--- Comment #3 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
This is a latent problem in ifcvt, that pulls the computation involving the
uninitialized k out of the always-false condition. Things go down the hill
when k's default def gets coalesced with b, and rtl optimizers further mess
things up.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/68083] [6 Regression] wrong code at -O3 on x86_64-linux-gnu
2015-10-24 22:58 [Bug tree-optimization/68083] New: wrong code at -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu
` (2 preceding siblings ...)
2015-10-30 11:03 ` aoliva at gcc dot gnu.org
@ 2015-10-30 11:18 ` aoliva at gcc dot gnu.org
2015-10-30 13:05 ` rguenth at gcc dot gnu.org
2015-10-30 13:16 ` aoliva at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: aoliva at gcc dot gnu.org @ 2015-10-30 11:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68083
--- Comment #4 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
s/ifcvt/ifcombine/ above, sorry
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/68083] [6 Regression] wrong code at -O3 on x86_64-linux-gnu
2015-10-24 22:58 [Bug tree-optimization/68083] New: wrong code at -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu
` (3 preceding siblings ...)
2015-10-30 11:18 ` aoliva at gcc dot gnu.org
@ 2015-10-30 13:05 ` rguenth at gcc dot gnu.org
2015-10-30 13:16 ` aoliva at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu.org @ 2015-10-30 13:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68083
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu.org
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ok, we shouldn't introduce uninitialized uses. It's going to be interesting to
teach this to ifcombine ;)
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/68083] [6 Regression] wrong code at -O3 on x86_64-linux-gnu
2015-10-24 22:58 [Bug tree-optimization/68083] New: wrong code at -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu
` (4 preceding siblings ...)
2015-10-30 13:05 ` rguenth at gcc dot gnu.org
@ 2015-10-30 13:16 ` aoliva at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: aoliva at gcc dot gnu.org @ 2015-10-30 13:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68083
Alexandre Oliva <aoliva at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |aoliva at gcc dot gnu.org
--- Comment #6 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
Created attachment 36622
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36622&action=edit
Patch I'm testing to fix the problem
This patch stops ifcombine from introducing this kind of undefined behavior.
I'm testing it now, and I'll post it to the list if that completes
successfully.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2015-10-30 13:16 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2015-10-24 22:58 [Bug tree-optimization/68083] New: wrong code at -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu
2015-10-26 11:42 ` [Bug tree-optimization/68083] [6 Regression] " rguenth at gcc dot gnu.org
2015-10-26 11:56 ` mpolacek at gcc dot gnu.org
2015-10-30 11:03 ` aoliva at gcc dot gnu.org
2015-10-30 11:18 ` aoliva at gcc dot gnu.org
2015-10-30 13:05 ` rguenth at gcc dot gnu.org
2015-10-30 13:16 ` aoliva at gcc dot gnu.org
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